24 research outputs found
Lawson criterion for ignition exceeded in an inertial fusion experiment
For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion
Infuence of mass ablation on ignition and burn propagation in layered fusion capsules
After decades of research, recent laser-driven inertial fusion experiments
have demonstrated rapid progress towards achieving thermonuclear ignition using
capsule designs with cryogenic fuel layers. The ignition physics for these
layered capsules involves a complex interplay between the dynamically forming
hot spot and the dense surrounding fuel. Using analytic theory, we demonstrate
that the mass ablation rate into the hot spot depends sensitively upon the
temperature of the dense fuel, resulting in ablative inflows up to 4x faster
than previous estimates. This produces an enthalpy flux into the hot spot which
plays a critical role in controlling the hot spot temperature, the ignition
threshold, and the subsequent burn propagation. The net influence of mass
ablation on the ignition threshold is regulated by a dimensionless parameter
which depends upon the temperature of the dense fuel. As a consequence, the
ignition threshold is sensitive to any mechanism that heats the dense fuel,
such as neutrons or radiation emitted from the hot spot. These predictions are
confirmed using radiation hydrodynamic simulations for a series of capsules
near ignition conditions. This analysis may have relevance for understanding
the variable performance of recent experiments and for guiding new capsule
designs toward higher fusion yields.Comment: 10 pages, 6 figure
Automated dating of the world's language families
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94255-OA.pdf (publisher's version ) (Open Access)35 p
Automated dating of the world's language families based on lexical similarity
This paper describes a computerized alternative to glottochronology for estimating elapsed time since parent languages diverged into daughter languages. The method, developed by the Automated Similarity Judgment Program (ASJP) consortium, is different from glottochronology in four major respects: (1) it is automated and thus is more objective, (2) it applies a uniform analytical approach to a single database of worldwide languages, (3) it is based on lexical similarity as determined from Levenshtein (edit) distances rather than on cognate percentages, and (4) it provides a formula for date calculation that mathematically recognizes the lexical heterogeneity of individual languages, including parent languages just before their breakup into daughter languages. Automated judgments of lexical similarity for groups of related languages are calibrated with historical, epigraphic, and archaeological divergence dates for 52 language groups. The discrepancies between estimated and calibration dates are found to be on average 29% as large as the estimated dates themselves, a figure that does not differ significantly among language families. As a resource for further research that may require dates of known level of accuracy, we offer a list of ASJP time depths for nearly all the world's recognized language families and for many subfamilies. © 2011 by The Wenner-Gren Foundation for Anthropological Research. All rights reserved
Automated dating of the world's language families based on lexical similarity
This paper describes a computerized alternative to glottochronology for estimating elapsed time since parent languages diverged into daughter languages. The method, developed by the Automated Similarity Judgment Program (ASJP) consortium, is different from glottochronology in four major respects: (1) it is automated and thus is more objective, (2) it applies a uniform analytical approach to a single database of worldwide languages, (3) it is based on lexical similarity as determined from Levenshtein (edit) distances rather than on cognate percentages, and (4) it provides a formula for date calculation that mathematically recognizes the lexical heterogeneity of individual languages, including parent languages just before their breakup into daughter languages. Automated judgments of lexical similarity for groups of related languages are calibrated with historical, epigraphic, and archaeological divergence dates for 52 language groups. The discrepancies between estimated and calibration dates are found to be on average 29% as large as the estimated dates themselves, a figure that does not differ significantly among language families. As a resource for further research that may require dates of known level of accuracy, we offer a list of ASJP time depths for nearly all the world's recognized language families and for many subfamilies. © 2011 by The Wenner-Gren Foundation for Anthropological Research. All rights reserved
Automated dating of the world's language families based on lexical similarity
This paper describes a computerized alternative to glottochronology for estimating elapsed time since parent languages diverged into daughter languages. The method, developed by the Automated Similarity Judgment Program (ASJP) consortium, is different from glottochronology in four major respects: (1) it is automated and thus is more objective, (2) it applies a uniform analytical approach to a single database of worldwide languages, (3) it is based on lexical similarity as determined from Levenshtein (edit) distances rather than on cognate percentages, and (4) it provides a formula for date calculation that mathematically recognizes the lexical heterogeneity of individual languages, including parent languages just before their breakup into daughter languages. Automated judgments of lexical similarity for groups of related languages are calibrated with historical, epigraphic, and archaeological divergence dates for 52 language groups. The discrepancies between estimated and calibration dates are found to be on average 29% as large as the estimated dates themselves, a figure that does not differ significantly among language families. As a resource for further research that may require dates of known level of accuracy, we offer a list of ASJP time depths for nearly all the world's recognized language families and for many subfamilies. © 2011 by The Wenner-Gren Foundation for Anthropological Research. All rights reserved